It is often necessary to introduce a secondary fluid, such as medication, into a fluid that is being supplied to a patient intravenously. Several devices are known for this purpose. One category of such devices uses a membrane that is designed to be pierced by a hypodermic needle. Because of the dangers associated with sharp objects that can injure healthcare workers, however, injection sites that do not require the use of needles are more desirable.
One such device is shown in U.S. Pat. No. 3,416,567 (Von Dardel et al.) where a resilient sleeve seals a feed-in orifice until the pressure of the secondary fluid is large enough to push the sleeve away from the orifice to allow the secondary fluid to enter the stream of the primary fluid. A device of similar construction is shown in U.S. Pat. No. 3,085,549 (Kacsuta).